Which of the Following Studies Apply to This: Subjects Were

Multiple Choice

which of the following studies apply to this: Subjects were children enrolled in a health maintenance organization. At 2 months, each child was randomly given one of two types of a new vaccine against rotavirus infection. Parents were called by a nurse two weeks later and asked whether the children had experienced any of a list of side-effects?

A) Observational cohort
B) Experimental.
C) Observational case-control
D) Observational cross-sectional.